Think about what was or is important to you when you were or are living according to your own ideas and rules. All of us slip from time to time and that is why I stated that last sentence with past and present tense. During those times how do you think? Are you thinking more about what would benefit you than what God would have you to do? Do you think more about how you want things to be for your comfort or do you think about what would bring glory to God? Are you more concerned during those times about climbing the ladder of success instead of defining success from God's point of view?
I think this is what Peter is driving at. Obedient children of God fashion themselves according to God's purpose...holiness, not according to their own fleshly desires. That's not to say we attain perfection by any means, but we should simply live with a conscience toward God and He will sanctify us and make us holy, fit vessels for His use.